I'm no nutritionist. Don't even play one on the the Internet (though I've made a few videos). But I do get asked a lot about foods and eating and why I'm a vegetarian (see the link above). I'll share here a few things that work for me; you will have to see what works for you.

Drink a LOT of water. Don't drink anything else. I will drink Gatorade if/when I run 7+ miles to replenish electrolytes faster. Other than that I don't drink anything else - no fruit juices, sodas, flavored waters. Just a lot of water. You'll know you're drinking "enough" water when your piss is clear like water.
Eat 4oz or more of greens per day. I eat bags of organic spinach that I buy at Whole Foods - one per day. Greens like spinach, kale, arugula, Swiss chard and others have strong nutritional benefits which you can Google and read about.
Bananas pre-workout, meals after. Any form of exercise I do, I have at least 4 hours of no-meal time before I begin. The only thing I eat before will be 2 bananas. They digest quickly, are a solid source of carbs, and they're sugary for those who, like me, enjoy sweets.
Gradually employ fruit to replace candy. I used to eat a ton of candy. Now I eat it very little, replacing those cravings with fruits which have their own sugars. I prefer red apples, strawberries, grapes, peaches and plums.

Don't forget the water.